iwn0 wifi driver error

I have intel wifi card on Dell laptop which works as device iwn0.
For some reason if the wifi signal goes off, such as router being switched
off, whenever the signal comes back, the interface usually reconnects to
the network automatically.
On one or two occasions it happened otherwise. After the router was
switched on again, the interface wasn't up again and had to be manually
restarted.
Following was the error seen in dmesg:
iwn0: fatal firmware error
Any leads?
Mayuresh.